I used to make my own potting mix from scratch, but last season I got a few yards of “garden mix” delivered, and for potting mix I just cut that with coarse perlite (~30% perlite), mixing in my wheelbarrow as needed. Here’s the recipe for the garden mix published on the website of the local company that delivered it:
- 30% soil
- 35% aged compost (municipal source)
- 25% “Moo Doo” (aged steer manure mixed with sawdust)
- 10% sand
It works pretty well as a potting mix when mixed with perlite, and the compost includes lots of partially decomposed wood chips/bark to add coarse texture other than the perlite. The municipal compost has the potential to be contaminated with pesticides or worse, but other than picking out bits of plastic I haven’t noticed anything along those lines.
I don’t sterilize for seed starting, and rarely notice any issues with most types of seeds. The only ones where I’ve had trouble with damping off are passifloras and papayas, never really any issues with garden seeds like tomatoes, peppers, cucurbits, or the various fruit trees I’ve started from seed.